Medical waste disposal is of urgent concern because the waste may cause infection. Such infectious waste is a by-product of medical and veterinary care. For example, regulated medical waste consists of the following categories:
1. Cultures and stocks of infectious agents and associated biologicals;
2. Pathological wastes;
3. Human blood and blood products;
4. Contaminated xe2x80x9csharpsxe2x80x9d, including needles, syringes, blades, scalpels, and broken glass;
5. Animal waste;
6. Isolation waste, including gloves and other disposable products used in the care of patients with serious infections; and
7. Unused xe2x80x9csharpsxe2x80x9d.
Hospitals typically segregate these categories of waste into three general groups: a) general medical waste, including waste listed above in categories 1, 2, and 3; b) veterinary waste, or category 5; and c) waste that is predominantly plastic, including categories 4 and 6. Contaminated sharps and isolation waste are categories of special concern, as this waste may have been exposed to highly dangerous infections such as AIDS or hepatitis. Sharps in particular have caused deep public concern when observed on beaches and other public areas.
Hospitals and other generators of medical and veterinary waste employ three main methods of waste handling: 1) on-site incineration of the waste, 2) on-site steam autoclaving of the waste and later shipment to a landfill, and 3) no on-site processing before turning the waste over to a waste hauler.
Predominantly located in urban areas, many hospital incinerators emit pollutants at a relatively high rate. In the emissions of hospital incinerators, the Environmental Protection Agency (EPA) has identified harmful substances, including metals such as arsenic, cadmium, and lead; dioxins and furans; organic compounds like ethylene, acid gases, and carbon monoxide; and soot, viruses, and pathogens. Emissions from these incinerators may be a bigger public health threat than improper dumping. (Stephen K. Hall, xe2x80x9cInfectious Waste Management: A multi-faceted Problem,xe2x80x9d Pollution Engineering, 74-78 (August 1989)).
Although steam autoclaving may be used to disinfect waste before further processing, it is expensive and time-consuming. Heat rapidly inactivates viruses; but bacteria survive somewhat longer than viruses. Bacterial spores can be highly resistant to heat sterilization. To assure effective disinfection, temperature monitoring devices such as thermocouples and biological indicators such as heat-resistant Bacillus stearothermophilus spores may be used.
U.S. Pat. No. 2,731,208 to Dodd teaches a steam-sterilizing apparatus for disposing of contaminated waste which shreds waste (xe2x80x9cincluding paper containers such as used sputum cups,xe2x80x9d Col. 1, lines 28-29), blows steam into a container full of shredded waste and pours the disinfected waste into a sewage system. This process has several drawbacks, including processing of only limited types of items and depositing the processed waste into a sewer (Col. 4, line 49).
Soviet Union Inventor""s Certificate No.1,123,703 also discloses a method of sterilizing medical instruments for reuse by UHF treatment. For injection needles it discloses a final temperature of 160xc2x0 to 470xc2x0 C. and for acupuncture needles it discloses a final temperature of 160xc2x0 to 270xc2x0 C.
U.S. Pat. No. 3,958,936 to Knight teaches compaction of hospital waste for more efficient landfill disposal. Specifically, this reference teaches the application of heat in the range of about 400xc2x0 to 600xc2x0 F. to hospital and other waste to melt the plastic and turn it into a hard, compact block for safer disposal in landfills. The waste is disinfected and needles become imbedded in the plastic. This method has the disadvantages of requiring high energy expenditure to attain high temperatures and landfill disposal.
U.S. Pat. No. 3,547,577 to Lovercheck discloses a portable device for treating garbage such as trash, domestic refuse and the like (Col. 1, lines 13-19). The machine shreds garbage, compresses the shredded garbage into briquettes, and sterilizes the briquettes with ethylene oxide gas (Col. 1, lines 15-19). After shredding, the garbage may be separated into magnetic and non-magnetic portions (Col. 2, lines 13-23). After the garbage is so separated, only the non-magnetic portion is compressed into briquettes and sterilized (Col. 2, lines 23-25). The sterilization step employs ethylene oxide gas which requires temperature control (Col. 2, lines 30-57). Thus, the briquettes are maintained at a temperature of about 54xc2x0 C. (Col. 2, line 51). A drawback of this system is that both heat and poisonous gas are required to disinfect the garbage. Another drawback is that when the waste stream is divided into metal, water and briquettes, only part of the waste stream (the briquettes without metal or water) is disinfected. An additional disadvantage is that the volume of the waste stream is limited in that only one briquette is formed at a time. Another drawback is that the material is disposed in a landfill or by incineration. Although use as a fertilizer is suggested (Col. 1, line 47), there is no teaching that the briquettes are really suited for that use or how the briquettes could be further processed for that use.
Various energy sources are being considered as potential sterilants. Microwaves are increasingly being investigated for rapid sterilization of individual medical devices and shredded medical waste. Recently, an experiment showed that metallic instruments could be disinfected in only 30 seconds in a microwave chamber. (N.Y. Times, xe2x80x9cScience Watch: Microwave Sterilizer is Developed,xe2x80x9d Jun. 20, 1989). A problem is that this particular method can handle only a few instruments at a time.
According to one publication, a medical waste disposal system utilizing microwaves has apparently been developed. This system first shreds medical waste, sprays it with water and spreads the small pieces in a thin layer on a conveyor belt. Then, the conveyor carries the mixture through a microwave chamber which heats the mixture to about 96xc2x0 C.
The waste can be routed to a steaming station where steam is applied to inactive surviving microorganisms. After the disinfection step, the waste is packaged for shipment to landfills or incinerators. (The Wall Street Journal, p. B3, Apr. 10, 1989).
Further, microwaves are limited in their penetration. If applied to large-scale, boxed medical waste, the microwaves alone do not heat very effectively. In contrast, radio-frequency (RF) waves are relatively low-frequency waves which penetrate more effectively. RF waves have been used directly and indirectly for sterilization.
U.S. Pat. No. 3,948,601 to Fraser et al. teaches the indirect use of RF waves in disinfecting a wide variety of medical and hospital equipment as well as human waste. This reference teaches the use of RF waves to heat certain gases (particularly argon) to ionize into gas plasma at approximately 100xc2x0 to 500xc2x0 C. This references teaches that xe2x80x9ccoolxe2x80x9d plasma (Col. 1, line 12) effectively sterilizes an article at a temperature of only 25xc2x0 to 50xc2x0 C. and very low pressure. However, sterilization by plasma gas does not suggest the direct use of RF waves in sterilization.
Whether or not the hospital first autoclaves its medical waste, including broken needles and glass, the waste is then turned over to a waste handler for transport to a landfill or other depository. There are several problems with this disposal method. First, landfills, particularly in many urban areas, are becoming filled. In addition, older landfills may leak toxic chemicals into the surrounding earth and contaminate the water supply. Thus, burying wastes is becoming more of a concern. Also, unauthorized dumping may occur.
One aspect of the present invention relates to a method of processing medical waste which includes the steps of continuously feeding medical waste into a tube and exposing the medical waste passing through the tube to electromagnetic radiation so as to heat and disinfect the medical waste.
A second aspect of the present invention relates to an apparatus for processing medical waste with an extruder that receives medical waste and forms a continuous tube of the medical waste for feeding through a source of electromagnetic radiation. The source of electromagnetic radiation receives the continuous tube of the medical waste and generates electromagnetic radiation that heats and disinfects the continuous tube to produce a disinfected continuous tube of the medical waste.
A third aspect of the present invention relates to a method of reducing the potential of ignition of a fire of a material to be disinfected by radio-frequency radiation by providing a material to be disinfected and continuously feeding the material into a tube, wherein a portion of the tube is positioned in a field of radio-frequency radiation. The material passing through the tube is exposed to the radio-frequency radiation so as to heat and disinfect the material.
Each aspect of the present invention provides an efficient apparatus and method to reduce the infectious potential of medical waste and to transform it into material which would not adversely impact the overall environment. The present invention provides improved throughput of medical waste per unit volume in addition to improved reduction of arcing, ignition of fires and radio-frequency field enhancements. Each aspect of the present invention also provides improved thermal performance by creating steam thereby pre-heating the material which aids in sustaining the material""s temperature. In addition, a preferred embodiment of the present invention allows for further transformation of pre-sorted medical and veterinary waste into either recycled plastic or refuse-derived fuel.
Additional advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.